Finally, and with acknowledgement of the inadequacies of the literature to date, we advance a tentative classification of these disorders into three groups, based on the reported severity of their cognitive impairments, and correlated with their neuropathological topography and MRI findings: group 1-SCAs 6 and 8-mild dysexecutive syndrome based on disruption of cerebello-cortical circuitry; group 2-SCAs 1, 2, 3, and 7-more extensive deficits based largely on disruption of striatocortical in addition to cerebello-cerebral circuitry; and group 3-SCA 17 and DRPLA-in which cognitive impairment severe enough to cause a dementia syndrome is a frequent feature.
The SCA17 clinical phenotype includes characteristics associated with cerebellar and cortical atrophy such as ataxia, dementia, epilepsy, chorea and parkinsonian features.